Around 100 paedophiles have been chemically castrated under a Government scheme to stop them reoffending.

The sex offenders volunteered to take drugs designed to stifle their libido during a pilot experiment at HMP Whatton in Nottinghamshire.

The drug reduces their testosterone levels to that of a prepubescent boy for a three-month period. After that, it wears off.

Potential subjects: The drug could be used on Whatton inmates such as sex offender Neil Wilkinson, left, or Victor Kelly, right, who offered a 12-year-old cocaine to have sex with him

The ongoing experiment could revolutionise the way the British penal system deals with sick criminals incarcerated at Whatton.

These have included rapist Neil Wilkinson, who later killed his cellmate, and paedophile Victor Kelly, 62, who offered a 12-year-old cocaine to have sex with him.

The drug is already mandatory for child sex offenders in Poland, Russia and certain U.S. states.

WHAT IS CHEMICAL CASTRATION?

Chemical castration involves a man taking hormones that suppress the production of testosterone, leading to a decreased sex drive.

Poland introduced mandatory chemical castration for some sex offenders in 2009, it was introduced in South Korea in September and Russia and Moldova are following suit.

Both Germany and the Czech Republic have been criticised by Europe's top human rights body for using voluntary surgical castration to treat sex offenders.

It could become the norm in Britain as treatment for notorious criminals such as Roy Whiting, who murdered eight-year-old Sarah Payne in 2000, or Colin Blanchard, who ran the online child sex network that included nursery worker Vanessa George.

The programme at HMP Whatton, a specialist category C prison which holds male sex offenders, has been run by the Prison Service and the Department of Health since 2009, and is co-ordinated by criminal psychiatrist Professor Don Grubin.

'I have referred around 100 people for treatment,' he told The Daily Mirror - a figure that includes offenders who are being given the drug while in the community, as part of a scheme which has been running since 2007.

'We know the treatment works to reduce sexual arousal and fantasies.'

Chemical castration can cut the rates of reoffending from 40 per cent to five per cent, according to researchers in Scandinavia.

The medication is intended for use on those with compulsive or impulsive urges to offend and those who have difficulties in controlling sexual arousal, intrusive sexual fantasies or urges, sadism or other 'dangerous' tendencies such as necrophilia.

The prison now hopes to extend the voluntary scheme beyond the end of the year.

Evil: Roy Whiting, killer of eight-year-old Sarah Payne, could be one of the subjects on whom chemical castration is used

One drug used, leuprorelin (marketed as Prostap) inhibits the typically high sex drives of paedophiles by limiting the production of testosterone.

But the manufacturers admit it is likely that 'only small numbers of sex offenders will benefit from these treatments.'

Psychologist Dr Ludwig Lowenstein backed chemical castration, emphasising that a child's right to protection was much more important than the freedom of paedophiles.

He said: 'Apart from lengthy jail sentences, the only other way to deal with most of these people is through chemical castration.

'The idea of giving sexual offenders a pill to destroy their ability to have intercourse always provokes fierce objections on the grounds of civil liberties.

'But a child's right to protection is far more morally important than the freedoms of paedophiles.'

But Juliet Lyon, director of the Prison Reform Trust, said: 'It's difficult to see why anyone would invest public money in controversial medication when you could fund sex offender treatment in prison, police and public protection on release, all of which are proven to reduce reoffending.'

Ex-offenders: The drugs could be used on men like Barry Wade, left, who was jailed at Whatton for offences against two young girls, and Stan Carberry, right, who was imprisoned there for sex attacks on children as young as ten

WHO WILL THE DRUG BE USED ON?

Inmates of Whatton prison include:

Victor Kelly - a 62-year-old who offered a 12-year-old girl cocaine so she would have sex with him

Kevin Skaith - a prisoner who was jailed for possessing nearly 120,000 images of children demanded more 'educational' Sky channels at the facility

Neil Wilkinson - a sex offender who was cautioned for activity with a child and raped a man was charged with the murder of cellmate Stephen Hartley in 2008

Barry Wade - jailed for seven years for offences against two young girls

Stan Carberry - attacked children as young as ten. He and Wade were two of several former inmates who later went to live in Skegness - sparking fears of a paedophile ring being formed in the area

A Ministry of Justice spokesman said: 'We support the use of pharmaceutical interventions for high risk sex offenders given the evidence that it can be useful in reducing risk for some perpetrators.'

HMP Whatton has come in for its fair share of criticism over the years.

In May 2010, convicted paedophile Kevin Skaith demanded that more highbrow channels be made available at the facility.

The 43-year-old, who was serving a three-and-half year sentence for possessing nearly 120,000 images of children, complained that his options were limited to 'soap, sex and sport'.

In 2007, the prison was condemned for offering inmates cash bonuses for good behaviour during a staff strike, and a year earlier, up to £5,000 of taxpayers' money was put aside for quiz prizes.

There was further controversy when a prison officer at the institution was suspended for allegedly intimidating a prisoner with a baton.